Robust regression estimators have been proven to be more reliable and
efficient than least squares estimator especially when the data are contaminated
with influential observations. Since the influential data points greatly influence
the estimated coefficients, standard errors and test statistics, the usual statistical
procedure may be most inefficient as the precision of the estimator has been
affected. Several different robust regression estimators exist. Two of the most
commonly considered are: LAD-estimators and LMS-estimators.